Method of mouldig hollow rubber articles

ABSTRACT

A method for molding a hollow rubber article in which the article is formed as two separate halves of uncured rubber, the halves having locking sprues to prevent their displacement, the mould is pressurized with gas and the halves are then brought together and jointed and cured.

METHGD OF MOULDING HOLLOW RUBBER ARTICLES Filed Nov. 15, 1971 8 Sheets-Sheet l July 23, 1974 E. HOLROYD ET AL 3,825,457

METHOD OF MOULDING HOLLOW RUBBER ARTICLES Filed Nov. 15, 1971 8 Sheets-Sheet July 23, 1974 E. HOLROYD ET L 3,325,457

METHOD OF HOULDING HOLLOW RUBBER ARTICLES 8 Sheets-Sheet 5 Filed Nov. 15, 1971 July 23, 1974 E. HOLROYD ET AL 3,825,457

METHOD OF HOULDING HOLLOW RUBBER ARTICLES Filed Nov. 15, 1971 8 Sheets-Sheet :1

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July 23, 1974 E. HOLROYD ETAL 3,825,457

METHOD OF HOULDING HOLLOW RUBBER ARTICLES Filed Nov. 15, 1971 8 Sheets-Sheet 5 FIG. ll.

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July 23, 1974 E. HOLROYD ET AL 3,825,457

METHOD OF MOULDING HOLLOW RUBBER ARTICLES Files Nov. 15, 1971 8 Sheets- Sheet e July 23, 1974 E. HOLROYD ET AL 3,825,457

METHOD OF HOULDING HOLLOW RUBBER ARTICLES Filed Nov. 15, 1971 8 Sheets-Sheet '7 47 A so FIGJS.

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July23, 1974 E. HOLROYD ET AL 3,325,457

METHOD OF MOULDING HOLLOW RUBBER ARTICLES Files Nov. 15, 1971 s Sheets-Sheet United States Patent M 3,825,457 METHOD OF MOULDING HOLLOW RUBBER ARTICLES Eric Holroyd, High Legh Park, near Knutsford, Anthony G. Goodfellow, Maghull, near Liverpool, and James N. McGlashen, Winstanley, near Wigan, England, assignors to Dunlop Limited, Erdington, Birmingham, England Filed Nov. 15, 1971, Ser. No. 198,812 Claims priority, application Great Britain, Nov. 23, 1970, 55,586/70 Int. Cl. B29c N00 US. Cl. 156147 9 Claims ABSTRACT OF THE DISCLOSURE A method for moulding a hollow rubber article in which the article is formed as two separate halves of uncured rubber, the halves having locking sprues to prevent their displacement, the mould is pressurized with gas and the halves are then brought together and joined and cured.

This invention relates to the moulding of articles from fiowable, curable elastomeric materials, i.e. rubbery materials. It is concerned in one aspect with moulding techniques in which an article is formed by the joining together in a mould two or more separately formed parts. In another aspect, the invention is concerned to provide a means of locating and retaining the separately formed parts within the mould so that they are not displaced in an undesired manner before being joined together.

The invention is particularly concerned to provide a satisfactory means of moulding hollow rubber articles, for example hoses, tires and playballs, e.g. squash ball and tennis ball cores. Thus it will be appreciated that the invention is not limited to the manufacture of completely enclosed hollow articles but is also applicable to articles, e.g. hoses, that cannot conveniently be made as a unitary moulding.

There are many difficulties and disadvantages in conventional methods of forming many types of hollow rubber articles. For example, semi-solid or cushion tires are conventionally made by extruding, for example, a circular cross-sectioned strip of the desired rubber composition containing an off-center bore. The strip is cut to the desired length and the ends of each length are joined together to form a tire. The bore then forms a hollow enclosed passage inside the otherwise solid body of the tire. This type of extrusion is difiicult to control. It is also disadvantageous to form a tire by bending a strip into a circle since the inner circumference of the tire will be under compression and the outer circumference will be stretched. Similarly the moulding of tennis ball cores has a number of disadvantageous steps. These cores are conventionally made by moulding two separate hemispherical rubber halves, removing the halves from the mould, butting and applying adhesive to the rims of the halves, assembling pairs of adhesive-coated halves in a further mould and then securely joining them together.

The method of the present invention aims to provide an improved method of moulding which can be applied to a wide variety of enclosed and non-enclosed hollow articles and which can eliminate many of the difiiculties and timeconsuming steps of prior art manufacturing methods.

Accordingly in one embodiment the invention provides a method of moulding a hollow rubber article in which the article is first formed in two halves, each half being moulded in a female mould cavity from rubber in an uncured state, each half being provided with a locking sprue to prevent displacement of the half, the mould is pressurized and the two halves of the article are then 3,825,457 Patented July 23, 1974 brought into contact and joined together under heat and pressure.

The rubber may be any elastomeric, cross-linkable polymeric material, for example natural rubber, butylrubber, S.B.R., neoprene, ethylene-propylene rubber and nitrile rubber. The type of rubber used will of course depend on the desired properties of the finished article and the selection of a suitable rubber for any particular purpose is a well known procedure in the field of rubber technology.

Although the rubber is to be substantially uncured when used to form the halves, it is preferred to subject it to a certain amount of working prior to the forming steps in order to destroy its nerve or memory. Suitable working may be, for example, by milling, extrusion or other mechanical or heat treatment but should not be sufiicient to start the rubber on its curing cycle. In other words, although the rubber may have been subjected to a certain amount of energy, it is still substantially uncured when used to form the halves.

By the term halves in this specification is meant to embrace both uniform and non-uniform halves. Also it will be apparent that the method of the invention is applicable to the manufacture of article made from three or more parts as well as to articles made from two parts. Nevertheless it will be appreciated that uniform articles like cushion tires and tennis ball cores are most conveniently made by joining together two substantially identical arts.

p The mould is conveniently pressurized by the introduction of compressed air or other suitable gas, e.g. nitrogen. It is preferred to pressurize the mould by at least 5 pounds per square inch (p.s.i.) but considerably higher pressures may be used in certain circumstances. For example, where a completely enclosed hollow article is being made, it may be advantageous to make the finished article a pressurized article. Thus, for example, an inflated semi-solid or cushion tire or a pressurized tennis ball core can be made by joining the halves together under a suitable gas pressure. In order to obtain a satisfactorily pressurized tennis ball core, the mould can conveniently be pressurized by up to 25 p.s.i. prior to joining the halves. Even higher pressures may be desirable, e.g. for tires.

It will normally be convenient to pressurize the mould by allowing the gas under pressure to enter over the equator of the mould cavities. However, if male formers are used in conjunction with the mould cavities, it may in certain applications be advantageous to introduce the gas through the male formers, e.g. at their poles.

In a further embodiment the invention provides a moulding apparatus comprising at least one pair of female mould cavities, means to form moulded halves of rubber in those cavities, the cavities being provided with locking sprue grooves to prevent displacement of the halves, means to pre-work the rubber without any substantial curing prior to its being formed, means to pressurize the mould with gas and means to bring each pair of female mould cavities together to join their respective halves together.

The moulding of the halves into the female mould cavities may be carried out in any convenient manner. For example, male-plug forming, vacuum-forming and combinations of these two techniques may be used for sheet materials. Moreover, the moulding may be carried out by compression, transfer or injection moulding techniques.

The means to pre-work the rubber prior to forming may conveniently be the injection screw of an injection mould or the transferring action of a transfer mould. A combination of the two techniques can be employed whereby a transfer chamber is applied by a relatively low-temperature screw. For this reason compression moulding alone is not preferred for the method of the invention but it can be satisfactory if the rubber can be worked to the desired degree prior to being charged into the compression mould.

The locking sprues will be so shaped as to resist movement of the halves in the mould, for example due to shrinkage or to removal of male formers when the latter are used. The locking sprue may also be shaped to ensure that the compressed gas entering the mould passes over the lip and onto the surface of the moulded half which is to be the interior of the article but does not enter between the half and the wall of the female moulding cavity. This latter eflYect is undesirable since it causes blistering or similar blemishes on the product and can result in quite unsatisfactory products.

A particularly convenient form of locking sprue is one which consists of a thicker portion connected to the half of the article by a thinner portion. Examples of suitable locking sprues are shown in FIGS. 1, 2 and 3 of the accompanying drawings and are described more fully below.

We have discovered that, as the two parts of the article to be joined together are formed of rubber, it is necessary to ensure that the rubber is not cured to any appreciable extent prior to the joining stage or the parts will not satisfactorily join together. However a certain amount of prior working of the rubber is, as indicated above, desirable provided that it does not cause any curing of the rubber. The amount of prior working that can safely be used will of course depend on the particular rubber composition being employed but it is a fairly routine matter to ensure that for any particular system the parts are not cured prior to joining.

The method of the invention enables uncured halves to be formed and then brought together without damage. If these uncured halves were formed without the steps of the present invention they would be very susceptible to damage and dislodgement. For example, the uncured halves would tend to stick to male formers as the latter were removed thereby resulting in unsatisfactory moulding. The method of the invention overcomes these difficulties as explained more fully below and enables satisfactory, unblemished mouldings to be achieved from substantially uncured halves. Prior methods of overcoming this problem have usually required at least partial curing of the halves to prevent their being damaged. These partially cured halves cannot then be satisfactorily joined together unless adhesive is used. The halves have then to be removed from the mould, adhesive applied and the adhesive-coated halves relocated in a mould and joined together. The present invention eliminates all these difliculties and extra steps.

A further advantage is that because the halves are brought together before any curing has commenced, they will be amenable to joining together i.e. the desired article can be formed, with a relatively low degree of mould pressure. It will be appreciated that many articles, e.g. tennis ball cores, should have walls of uniform thickness and that excess pressure used at the formation of the joint could result in an unacceptable product. In other words excess pressure can cause undesirable wall-thickening in the area of the joint.

As indicated above, where uncured halves are moulded, there will be a very strong tendency for them to be displaced or torn before they can be joined together, for example, they will tend to stick to the male formers when the latter are removed. Thus the positive means i.e. locking sprues, of retaining the halves in their respective cavities which are provided by this invention are very important. This technique can be further assisted by coating the male formers with a suitable non-stick material e.g. poly (tetrafluoroethylene).

Moreover, pressurized gas may be introduced into the mould at any convenient stage prior to the joining together of the two halves. However, it is advantageous to introduce the pressurised gas at an early stage in the moulding process and so it is preferred to introduce it shortly after the formation of the separate halves. Thus, where as in the preferred embodiment, the halves are formed between male formers and the female cavitied moulds, it is advantageous to introduce the pressurised gas before or as the male formers are removed from contact with the moulded halves.

Thus it will be seen that the combined use of a specially shaped locking sprue and the introduction of gas under pressure ensures that the uncured halves are held in position in the female formers while the male formers are removed. Any tendency of the halves to stick to the male formers and thereby be dislodged by them can therefore be overcome and an unspoiled and uninterrupted moulding cycle be obtained. Furthermore, by virtue of the shape of the sprues, the gas does not get behind the moulded halves and cause unwanted blemishes.

The method and apparatus of the invention can with advantage be employed to mould many different hollow rubber articles, both enclosed and unenclosed. Examples of typical articles include playballs, hose and tap connectors, i.e. hose-to-hose and tap-to-hose connectors including branched T-piece units; complete self-connecting hose units, e.g. water hoses, car radiator and heater hoses not requiring special clips inner tubes; tires, e.g. semisolid tires; rotary oil seals; self-contained pump units; spark plug connectors; bellows dust covers; hot-water bottles; hollow springs e.g. suspension mountings such as for engines, ballcocks; buoys and floats; fenders; energyabsorbing devices and rubber gloves. Many other applications of the invention where shaped rubber mouldings are required are also possible.

Various embodiments of the invention are illustrated in the accompanying drawings in which:

FIGS. 1, 2 and 3 are cross-sections through examples of suitably shaped sprues;

FIG. 4 is a cross-section through part of two moulded halves and illustrating a scarf joint;

FIGS. 5 and 6 are diagrammatic illustrations of one means of pre-working the rubber composition prior to moulding the halves;

FIGS. 7 and 8 are perspective views of a rotary mould, with parts cut away, illustrating the two forming positions in which the halves are first formed and are then joined together;

FIGS. 9 to 1 6 are diagrammatic illustrations of the stages in a complete transfer moulding cycle, in which two press moulds are used in sequence for continuous operation;

FIG. 17 is a sectioned view of one form of tire that can be made by the method of the invention;

FIG. 18 is a sectioned view of a hose or tap connector that can be made by the method of the invention; and

FIG. 19 is a similar view of a modified hose or tap connector.

In FIG. 1 the moulded half 20 is formed having a sprue 21. Sprue 21 has a cut-away surface 22 so inclined that pressurised gas introduced into the mould in the direction of arrow A will deflect over the cut-away surface and thereby will not get between the moulded half and the surface of the mould itself, i.e. the tendency for the gas to get between surface 28 i.e. the exterior of the finished product, of the moulded half and the surface of the mould itself is effectively reduced.

In FIG. 2 is shown a ditferently shaped sprue. This sprue is connected to the moulded half 20 by means of a narrow moulded portion or neck 23. Trimming of the finished moulded product is made easier by virtue of this narrow portion 23. Again the sprue has a cut-away surface 22 to control the flow of gas into the moulding.

FIG. 3 shows a particularly preferred type of sprue. This has all the features of the sprue of FIG. 2 but has been formed at a small angle X from the normal with the moulded half. X" can conveniently be up to 45. By this means the two sprues are prevented from joining together when the two halves are joined together. Joining together of the twosprues may cause undesirable joint deformation.

FIG. 4 shows a section through part of two moulded halves about to be joined together. Halves 24 and 25, with their sprues not shown have angled faces 26 and 27, thereby forming a scarf joint in the product.

FIGS. 5 and 6 show'a suitable pre-working arrangement in which the rubber to be formed is fed to the press mould 30 via a screw-feed 31 and a transfer mould 32. The rubber composition 33 is fed by the screw 31 to fill the transfer chambers 34 and ports 35 of the transfer mould 32. The rubber is kept below its curing temperature during this operation by means of heatsinks or cooling chambers 36. For example any heat generated can be carried away here by a liquid coolant. FIG. 5 shows the stage at which the transfer chambers and ports have been filled with the rubber composition from the screw-feed. FIG. 6 shows the next stage in which the transfer mould 32 is moved into position in the press mould 30 and the press has been closed, thereby transferring the rubber composition into mould cavities 37 of the press mould. By this means the halves of the desired article are formed from substantially uncured rubber, but the rubber has received the desired preworking before being moulded. The transfer mould can then be removed after pressurising the press mould and the halves joined together in the manner described above.

The rotatable mould shown in FIGS. 7 and 8 consists of an upper mould platen 80, a lower mould platen 81, a transfer chamber 82 and a pressure sleeves 83. Upper mould platen 80 contains a female mould cavity 84, a male former 85 and a blank cavity 86. Lower mould platen 81 similarly contains a female mould cavity 87, a male former 88 and a blank cavity 89.

In FIG. 7 the first position of the mould is shown where the mould is just about to be closed prior to the forming of a pair of halves of the desired article. It will be seen that, when closed, mould cavity 84 and male former 88 will come together thereby defining a mould cavity in which one of the halves can be formed. Similarly mould cavity 87 and male former 85 will come together, thereby defining a second mould cavity for the other half to be formed. Thus in order to form the two halves of the article, the mould is closed and the rubber to be formed is introduced into the mould cavities under pressure via transfer chamber 82 (the transfer ports not being shown).

When the two halves have been formed, mould platens 80 and 81 can be rotated with respect to each other until the second position shown in FIG. '8 is reached. In this position it will be seen that, when the mould is closed, the two mould cavities, each now containing a moulded rubber half (not shown), will be brought into contact. Also male formers 85 an 88 will be located in blank cavities 89 and 86 respectively. Thus the mould is then re-closed and the two moulded halves can thereby be joined together and cured. As the mould is contained within pressure-sleeve '83, it can be pressurised at any convenient stage, for example immediately after forming the separate halves. The rotation of the mould platens and the joining together of the halves can therefore be conducted under gas pressure.

It will be appreciated that this type of rotary mould can be enlarged to employ multi-cavity mouldings with automatic or semi-automatic operation.

FIGS. 9 to 16 illustrate a working embodiment based on transfer moulding for making tennis or squash ball cores, although it will be appreciated that the same moulding principles can be applied to many other articles. Two press moulds 40 and 41 are used in succession to give continuous operation. Each press mould contains two opposed sets of female mould cavities 42 carried on upper platen 48 and lower platen 49. Lower platen 49 can be raised towards upper platen 48 by means of ram 50. Two transfer moulding chambers 43 and 44 to carry the rubber charge are each located between two back-toback sets of male formers 45. These combined chambermale former transfer units 46, 47 are moveable in and out of moulds 40 and 41 between the opposed sets of female formers 42. Thus when unit 46 is in the load or charge position between the two moulds 40 and 41, unit 47 is within mould 41. Similarly when unit 47 moves to the charge position, unit 46 moves within mould 40.

FIG. 9 shows the first stage of the process. Transfer unit 47 is empty within mould 41 and transfer unit 46 is being charged with rubber. The means of charging the rubber into the transfer units may be any conventionally used, but a screw-feed as illustrated in FIGS. 5 and 6 is preferred. In FIG. 10, unit 46 has moved into mould 40 and unit 47 is now in position to be charged. In FIG. 11, ram 50 of mould 40 has raised platen 49 of that mould into contact with unit 46 until unit 46 is under pressure between platens 48 and 49. This pressure forces the rubber in transfer chamber 43 to be squeezed into the mould cavities defined between female parts 42 and male formers 45. Thus substantially uncured half shells 51 of the desired article are formed. While this is taking place, chamber 43 of unit 47 is charged with rubber.

The next stage, FIG. 12 shows mould 40 having been opened by lowering platen 49 by means of ram 50. Transfer unit 46 has been removed empty from mould 40 and charged transfer unit 47 has entered open mould 41. Mould 40 is preferably pressurised between the stages shown in FIGS. 11 and 12, i.e. before the male formers 45 on the transfer unit 46 are removed from contact with the formed halves 51.

FIG. 13 shows the ram 50 of mould 40 again raising platen 49 but this time into direct contact with upper platen 48. Thus the moulded half-shells 51 are brought together in pairs and the hollow cores 52 so formed are cured. Transfer unit 46 is re-loaded at this stage.

FIG. 14 shows mould 40 being opened by the lowering of ram 50 and the moulded ball cores 52 being extracted. Also at this stage ram 50 of mould 41 raises lower platen 49 of that mould to press unit 47 between platens 48 and 49. Thus half-shells 51 are now formed in mould 41.

FIG. 15 shows the stage corresponding to FIG. 12 in that ram 50 of mould 41 has now been lowered and unit 47 removed, leaving two opposed sets of moulded halfshells 51 in mould 41. Reloaded unit 46 has been recharged into position in mould 40. Similarly, the mould 41 is preferably pressurised before the unit 47 and its male formers 45 are withdrawn.

FIG. 16 shows ram 50 of mould 41 raising platen 49 into contact with platen 48 to join the half-shells together into ball cores 52 in that mould. At the same time ram 50 of mould 40 rises to press transfer unit 46 between platens 48 and 49 of that mould. Thus another series of halfshells 51 are formed.

The whole cycle can be repeated continuously. The extracted ball cores are collected and trimmed to remove their sprues (not shown).

FIG. 17 shows a section through a diameter of a typical semi-solid or cushion tire that can be made by the method of the invention. The tire is first moulded as two substantially uncured semi-toroidal halves 60 and 61. Half 60 is formed having, in this particular specific embodiment, two generally U-shaped channels 62 and 63 in its face to be joined to half 61. Half 61 has two corresponding channels 64 and 65 in its face to be joined to half 60. Half 61 additionally contains a valve inlet 66. The two halves 60 and 61 are brought into contact along line B so that the two pairs of U-shaped channels are brought together to from two recesses 67 and 68 running around and inside the tire. The two halves are then moulded together and vulcanised to form the desired tire. The sprues 69 around the joint lines are to be trimmed off and if desired one of the recesses 67 can be inflated via valve inlet 66 after insertion of a suitable valve.

FIG. 18 shows a sectional view of a tap-to-hose or hoseto-hose rubber connector that can also be made by the method of the invention. The connector has a generally barrel-shaped hollow body 70 having a, for example, circular orifice 71 at each end to give access to the interior of the body. Each end of the body is provided with a re-entrant lip-seal portion 72 of generally frustoconical shape. To connect to a tap or hose, the tap or hose is pushed into orifice 71 so that the lip-seal portion grips tightly onto it. Because of its specially shaped reentrant lip-seals and because it is formed from resilient rubber no clips are required to secure the connector to a tap or hose. Any medium under pressure, e.g. Water, being introduced into the connector via the tap or hose, will tend to exert pressure on the rear surfaces 73, of lip-seals 72, thereby holding the connector firmly in place. Thus, for example, a hosepipe can be firmly attached into one end of the connector and the other end of the connector can be attached to a tap. The connector is moulded in two identical halves 74 and 75 (sprues not shown) and the halves are joined along line C.

FIG. 19 shows a section through a similar connector but this time in the form of a T-branch or three-way connector. Thus a branched tube 76 is formed integrally with the body 70 to give three connections, two at orifices 71 and the third at the end of tube 76 remote from body 70. Again the connector is moulded in two identical halves 74 and 75 that are then joined together along line D.

The re-entrant lip-seal portions of these connectors could, if desired, be provided with internally-extending fins or serrations to aid the gripping of the lip-seal onto a tap, hose or the like.

Having now described our invention, what we claim is:

1. A method of making hollow rubber articles to join complementary parts of said articles and substantially eliminate undesirable wall thickening in localized areas, comprising the steps of:

mechanically working substantially uncured rubber to substantially destroy its memory;

forming the worked, substantially uncured rubber into at least two complementary parts of an article in female mold cavities with cooperating male formers, said complementary parts being formed with locking sprues to prevent displacement thereof in said cavity;

withdrawing said male formers from the cooperating female mold cavities;

pressurizing the mold cavities with a fluid under pressure prior to withdrawing said male formers;

bringing said complementary parts together at their respective edge portions; and

heating under conditions of pressure said complementary parts to cure them and join them together at said respective edge portions, thereby forming an adhesiveless joining of said complementary parts.

2. A method according to claim 1, in which said fiuid is introduced over the equators of said female mold cavities.

3. A method according to claim 1, in which said prior mechanical Working of said rubber is carried out by the screw of an injection mold.

4. A method according to claim 1, in which said prior mechanical working of said rubber is carried out by the transferring action of a transfer mold.

5. A method according to claim 1, in which said complementary parts are formed as unperforated parts and are joined with sulficient pressure to produce the finished article which is a completely enclosed hollow article containing gas at greater than atmospheric pressure.

6. A method according to claim 1, in which said looking sprues are each formed to have a thicker lip portion which is connected to its part of the article by a thinner portion.

7. A method according to claim 6, in which said fluid under pressure enters the mold over the lip of said locking sprue and into contact with that surface of each molded part which is to be the interior of the finished article.

8. A method according to claim 1, wherein said mechanical working step includes the further step of maintaining the temperature of said worked rubber below its curing temperature during said working step.

9. A method according to claim 8, wherein said pressurizing step comprises pressurizing said cavities with a pressure of at least five pounds per square inch.

References Cited UNITED STATES PATENTS 1,575,388 3/1926 Roberts 264-96 1,400,146 12/1921 Eggers et al. 264-96 1,404,320 1/1922 Roberts et al. 156145 3,477,101 11/1969 Fritsch 264-328 CHARLES E. VAN HORN, Primary Examiner F. FRISENDA, JR., Assistant Examiner US. Cl. X.R. 

